Electrical insulating oils



Patented July 1, 1947 ELECTRICAL INSULATING OILS Frank J. Soday, Swarthmore, Pa., assignor to The United Gas Improvement Company, a corporation of Pennsylvania No Drawing. Application February 10, 1943, Serial No. 475,440

12 Claims. 1

This invention relates to electrical insulating oils comprising certain high-boiling aromatic oils.

More particularly, this invention pertains to electrical insulating oils comprising the highoi aromatic Oils separated from tar formed during the production of combustible gas by processes involving the pyrolytic decomposition of petroleum oil with or Without the aid of catalysts.

An object of the invention is the provision of insulating oils possessing outstanding dielectric properties, the said oils comprising high-boiling aromatic oils separated from tar formed during the production of combustible gas by processes involving the pyrolytic decomposition of petroleum oil with or without the aid of catalysts. Another object of the invention is the incorporation of such high boiling aromatic oils in absorbent materials such as paper, cloth, and other organic fiber products, either alone or in combination with certain resinous and/r plasticmaterials, and the use of such oil-impregnated materials for electrical insulation purposes. Other objects and advantages of the invention will be apparent to those familiar with the art upon an inspection of the specification and claims.

The electrical insulating oils in use at the present time suffer from many disadvantages, chief among which may be mentioned their lack of stability under the usual operating conditions. This may be traceable, in most cases, to the presence of impurities in such oils and/or to the relatively small proportions of stable aromatic hydrocarbons present.

I have discovered that the aromatic hydrocarbon oil boiling above 210 C., said oil having been separated from the tar formed during the production of gas by processes involving the pyrolytic decomposition of petroleum oil, with or without the aid of catalysts, is unusually well adapted as an electrical insulating oil.

High-boiling aromatic oils having a preponderant portion boiling above approximately 250 C., and more particularly above 275 0., are pre" ferred. Excellent results are obtained in most cases by the use of such oils having a preponderant portion boiling above 300 C. For certain purposes, it may be preferred to employ high boiling aromatic oils of this type which boil substantially within certain ranges, for example, between 225 and 450 0., more preferably betweenv 2 250 and 400 C., and still more preferably between 275 and 450 C.

The excellent results obtained when such aromatic oils are used as electrical insulating oils are due largely to their exceptional stability characteristics under the most adverse operating conditions. This is particularly true when such oils are refined by processes to be more particularly described herein.

In addition, the excellent compatibility of aromatic oils of the type described, in conjunction with their exceptionally low viscosity characteristics greatly assists in any blending operations required. This is of particular value when preparing resin and/or plastic blends for use as insulating compositions.

Aromatic oils of the type described herein are extracted and/or distilled products, consequently they contain very little, if any, free carbon or other extraneous materials.

It has been discovered that very considerable quantities of high-boiling aromatic oils of the type described are contained in the tar produced in the vapor phase pyrolysis of crude petroleum oil or a fraction or fractions thereof such as, for example, gas oil or residuum oil. This is particularly so in the case of petroleum oil gas tar produced when the pyrolysis is conducted at relatively high temperatures, such for example as in the manufacture of oil gas or carburetted Water gas at average set temperatures above 1300 F. and also particularly so when the oil pyrolyzed is naphthenic, such as a crude oil classifiable in classes 5 to '7 inclusive, according to the method of classification described in Bureau of Mines Bulletin 291 as modified by Bureau of Mines Report of Investigations 3279, or a fraction or fractions of such an oil.

Recently, methods have been developed for the recovery of unusually large quantities of aromatic hydrocarbon material boiling in the ranges set forth, from petroleum oil gas tar, produced in the manufacture of gas, such for example, as carburetted water gas, oil gas, and the like. These methods recover high-boiling aromatic oils which are unique in character.

The usual distillation Procedures employed for the purpose of petroleum tar dehydration and/or tar fractionation have been such as to polymerize the readily heat polymerizable monomers above 210 C., which are frequently present in large proportions, into heavy polymers, which became inextricably mixed with the heavy black pitch constituents and the high-boiling non-heat polymerizable aromatic oils present. As a result, the high-boiling aromatic oils were retained by the residual tar or pitch.

In co-pending application Serial Number 370,- 608, filed December 18, 1940, by Edwin L. Hall and Howard R. Batchelder, which matured into Patent No. 2,387,259, granted October 23, 1945, the separation of the high-boiling aromatic hydrocarbon oils and heat polymerizable monomeric aromatic hydrocarbons boiling above 210 C. from the heavy black pitch constituents of the petroleum tar is described and claimed, together with heat polymers produced from said polymerizable oils.

In co-pending application 886,232, filed April 1, 1941, by Waldo C. Ault, which matured into Patent No. 2 337,237, granted October 23, 1945, there is described and claimed the production of catalytic resins from the heat polymerizable and/ or catalytically polymerizable monomeric hydrocarbons boiling above 210 C. and separated in monomeric form from the heavy black pitch constituents of the petroleum tar.

he high-boiling non-heat p-olymerizable aromatic oils of the type described may be isolated from the unpolymerized oils obtained from each of these processes.

In the manufacture of oil gas and carburetted water gas, the tar produced is usually in the form of an emulsion due to the condensation of hydrocarbon constituents from the gas in the presence of water simultaneously condensed from the gas or otherwise present.

In copending application 3423735, filed June 27, 1940 by Edwin L. Hall and Howard B. Batchelder, which matured into Patent No. 2,366.899, granted January 9, 1945, there is described a method of dehydrating such petroleum tar emulsions and of fractionating the hydrocarbon constituents thereof by rapid distillation with the separation from the heavy pitch constituents of residual tar of a mixture of nonheat polymerizable aromatic hydrocarbons and heat polymerizable unsaturated monomeric aromatic hydrocarbons boilin above 210 C.

In copending application 353,034, filed August 17, 1940, by Howard B. Batchelder, which Inatured into Patent No. 2383362, granted August 21, 1945. there is described the dehydration of such petroleum tar emulsions and the fractionation of the hydrocarbon constituents thereof with the recovery of monomeric unsaturated heat polymerizable hydrocarbon constituents and high-boiling non-heat polymerizable aromatic oils separate from the heavy black pitch constituents of residual tar, by the solvent extraction of the emulsion with a hydrocarbon solvent such as liquefied propane or butane.

Other processes, for example fractional condensation, might be employed to recover these high boiling aromatic hydrocarbons separate from the heavy black pitch constituents of the tar. Also processes for oil pyrolysis which avoid the formation of emulsions, may be employed for the production of the high-boiling aromatic hydrocarbons. Furthermore, while it may be preferred to employ petroleum oils or cuts there from, which are classifiable in classes 5 to 7 inclusive according to Bureau of Mines Bulletin 291 as modified by Bureau of Mines Report of Investigations 3279 and particularly in class 7, other oils may be employed.

As a result of separation of the light oil and higher-boiling aromatic oil components of the products of such petroleum oil pyrolysis from the residual tar, without polymerization or with materially reduced polymerization, a substantially pitch-free highly aromatic hydrocarbon material may be separated havin a portion boilwithin the range of from 210 to 400 C., or higher, which may contain from 5% to 30%, and higher, of monomeric unsaturated aromatic hydrocarbons readily po-lymerizable by heat.

As previously stated, the above mentioned heat polymerizable highly aromatic monomeric mate rial may be readily polymerized by heat to form resins, after which the high-boiling aromatic hydrocarbons may be separated from such resins by any desired method, such as by distillation, which may be assisted by steam and carried out under reduced pressures.

Polymerization may be effected by heating the total material separated from the residual tar suficiently to polymerize the readily heat polym rizable monomers boiling within the range of from 21 to 450 C., but insuihciently to appreciabl polymerize the heat polymerizable material contained in lower boiling ranges, such, for instance, as methyl styrenes and styrene. This may be accomplished, for example, by heating with stirring for 4 hours at 200 C., followed by distillation under vacuum to isolate the resin The higher-boiling non-heat polymerizable arcmatic oils then may be separated by fractional distillation.

It may be preferable, however, to first eiiect a separation by fractional distillation between light oil boiling between say, 210 C. and oils boiling above say, 210 C,

The polymerization of the heat polymerizable unsaturated monomeric material in the separated aromatic oils boiling above, say, 210 C. may be effected by heating the oil with stirring, for example, for four hours at 200 C.

The resin thus produced, together with any resin produced during the separation of the light oil from the higher-boiling oil, may then be removed by distillation under vacuum.

As hereinbefore stated, after polymerization the high-boiling non-heat polymerizable aromatic oils may be isolated from the resin by distillation in vacuum, which may be assisted by steam, or otherwise.

The high-boiling monomeric material derived from tar obtained in the pyrolysis of petroleum, by rapid distillation or solvent extraction methods, or otherwise, also may be polymerized prior to the separation of the desired high-boiling nonheat polymerizable aromatic oils by the application of certain catalysts, either with or without the simultaneous, or otherwise, application of heat, for example, as described and claimed in the above copendin application Serial Number 386,232, filed April 1, 1941, by Waldo C. Ault.

Catalysts such as mineral acids, for example, sulfuric acid, hydrogen chloride, acids of phosphorus, or acid-acting metallic halides or complexes of said halides, preferably organic solvent complexes, as for example, boron trifiuoride, aluminum chloride, boron trifiuoride-diethyl ether complex, boron trifiuoride-dimethyl ether complex, boron trifluoride-phenyl other complex, boron trifluoride-phenyl methyl ether complex, boron trifluoride-dioxan complex, boron triflu oride-toluene complex, correspondin aluminum chloride complexes, andthe like, may be; employed for this purpose.

The metallic halides and their complexes employed are characterized by their ability to hydrolyze in the presence of water to give, an acid reaction and, hence, for, convenience they may be termed acid-acting metallichalides.

While high-boiling oils of the type described may be isolated from the tar emulsion by either distillation or solvent extraction methods, as pointed out previously, I prefer to employ highboiling oils which have been isloated by solvent extraction methods because of the presence therein of very much larger proportions of highboiling aromatic oils. of the type desired. The flash-distillation method isolating such oils from the tar emulsion permits the polymerization of a considerable portion of the unsaturated materials to take place (though very greatly less than in conventional methods), thus increasing the quantity of resinous and/or pitch-like materials left behind in the tar. The presence of these polymers in the tar reduces the quantity of the aromatic oils recovered, and particularly those having the desired high boiling ranges.

While aromatic oils boiling above 210 C. may be produced by conventional methods of distillation of the products of vapor phase oil pyrolysis produced in the manufacture of gas, and may be employed in accordance with the presentinvention, such aromatic oils are by no means as preferred for this purpose, as are the high boiling aromatic oils produced by the use of separation methods which minimize polymerization of the high-boiling heat polymerizable unsaturates.

In conventional distillation. methods, the tars are subjected to elevated temperatures for such lengths of time as to polymerize the far greater part, if not all. of the high-boiling heat polymerizable unsaturates. This results in the production of very highly viscous mass, from which the removal of the higher boiling non-heat poly merizable aromatic constituents by commercially feasible methods is precluded by very great operating difllculties.

The processes which minimize or avoid polymerization in the separation of the high-boiling aromatic oil from the tar thus produce highboiling aromatic oils which differ from those produced by conventional processes not only in their content of high-boiling heat-polymerizable unsaturates, but also in their content of the higher boiling non-heat polymerizable aromatic constituents.

High boiling aromatic oils produced by these methods are therefore unique.

In connection with the isolation of these highboiling aromatic oils by the preferred method, namely, by the solvent extraction of the tar emulsion, it should be emphasized that the mixture of aromatic oils and unsaturated oils obtamed by such methods may be fractionally distilled prior to, during, or after polymerization to isolate the aromatic oils having the desired high boiling range. Separation by distillation prior to polymerization may be preferred in certain. cases for reasons more particularly set forth in said copending applications.

Thus, the extracted oils may be distilled prior to polymerization to give a fraction boiling above, say, 2'75-300 C., and a lower boiling fraction. These may be polymerized separately, after which the high-boiling aromatic oils of the type desired may be isolated from the resinous materials obtained.

The process may be further illustrated by the following examples.

Example 1 Petroleum oil gas tar emulsion obtained by the pyrolysis of a Bureau of Mines type 7 naphthenic oil in the presence of steam in a. ceramic chamber at temperatures above 1300 F. is extracted with liquid propane. After removal of the propane, the extracted oil is flashdistilled to give a fraction boiling almost entirely above 275 C.

This fraction is polymerized by heating to a temperature of 200 C. for a period of 4 hours after which the aromatic oils are isolated by distillation until a vapor temperature of approximately 200 C., or higher, is reached at a pressure of 20 mm. of mercury absolute.

Example 2 A sample of extracted and distilled oil similar to that employed in Example 1 is polymerized by the addition of 96% sulfuric acid in small portions at temperatures below 50 C. until no further temperature rise is noted. The addition of 1% by weight of acid usually is sufficient to insure complete polymerization.

The acid sludge layer then is removed, either with or without the addition of, naphtha to reduce the viscosity of the mixture, and the polymerized material washed and, neutralized. The high-boiling aromatic oils then are isolated by distillation under reduced pressure.

Example 3 A sample of extracted and distilled oil similar to that employed in Example 1 is polymerized by the addition of 3% by weight of aluminum chloride-diethyl other complex at temperatures below 50 C. After the polymerization has been completed, the catalyst is neutralized by the addition of an aqueous alkalinesolution. Clay or other desired filter aid then is added and the mass filtered. The filtered material is distilled under reduced pressures to isolate the high-boiling aromatic oils.

Any combination of the foregoing methods may, of course, be employed to isolate the highboiling aromatic oils.

Certain fractions of such oils cointain substantial proportions of relatively high-melting hydrocarbons, such as naphthalene, anthracene, and phenanthrene. While the presence of these materials is not disadvantageous from the standpoint of many electrical insulating uses, and is quite advantageous in certain cases, they may be removed, at least in part, if desired, by cooling to any desired. temperature, followed by filtration to remove the crystalline material.

The oils obtained may be employed for certain electrical insulating purposes without further treatment, if desired. However, I prefer to employ oils which have been further refined to more completely remove any unsaturated and/or reactive constituents present.

As a result of extensive experimentation, I have discovered that such aromatic oils may be refined in a satisfactory manner by the application of mineral acids, such as sulfuric acid, preferably of at least 94% concentration. While any desired proportion of acid may be employed, and the refining operations carried out in any desired manner, I generally prefer to agitate or otherwise intimately contact the said oil with one or more portions of sulfuric acid. The proportion of acid employed in each washing operation preferably is from 1 to 10%, and more preferably from 2 to by volume of the oil being treated. The acid washing operations preferably are conducted at temperatures below 40 C., and more preferably below 30 C.

Excellent results are obtained when aromatic oils of the type described herein are treated with from 3 to 30% by volume of from 95 to 100% sulfuric acid, the said treatment being carried out in one or more stages, at temperatures below 35 C. When the said acid treatment is carried out in more than one stage, the sludge formed in the previous acid treatment may be removed prior to the addition of fresh acid, if desired,

After removing the acid sludge from acid washed aromatic oils of the type described herein, the said oils preferably are treated to remove any acid residues and/or sludge present. This may be accomplished, among other ways, by agitation with one or more portions of an aqueous alkaline solution, such as a 5-20% sodium carbonate solution, followed by washing with one or more portions of water. If desired, the acidwashed oil may be washed with water alone to remove any acidic residues and/ or sludge, or such water washing may precede the alkaline washing described.

The acid-washed oil may be diluted with a lower-boiling oil of lower specific gravity, such as an oil boiling below 175 C., for example xylene, prior to alkali and/or water washing in order to permit the sludge present to settle in a more satisfactory manner. After the neutralizing operations have been completed, the lowerboiling oil or oils, may be separated from my refined high-boiling aromatic oil by distillation and or fractionating operations.

The acid-washed aromatic oils also may be neutralized by contacting with an adsorbent agent, such as silica gel, alumina, clay, diatomaceous earth, infusorial earth, and the like, for example Attapulgus clay, and such neutralizing operations may be carried out in a batch or continuous system and at room temperatures or elevated temperatures. Such treatment with absorbent agents may be carried out alone or in conjunction with aqueous alkaline washing and/or Water washing operations, if desired. When carried out in conjunction with alkaline and/or water washing operations, the treatment with absorbents preferably is carried out last in order to remove all traces of impurities from the said refined oils.

In the absence of such treatment with an absorbent agent, the acid-refined and neutralized oil may be distilled, if desired, to remove all traces of any non-volatile impurities present.

In certain cases, aromatic oils of the type described herein may be refined in a satisfactory manner by treatment with absorbent agents without resource to other refining operations. In general, however, I prefer to acid-wash such oils in order to more completely remove any unsaturated and/or reactive compounds present.

As pointed out previously, I have discovered that aromatic oils of the type described herein should preferably have the preponderant part boil above at least 250 C., and more particularly 275 C., when used for electrical insulation purposes. Excellent results are obtained when arematic oils of the type described, the preponderant part of which boil above 300 C., are employed.

In addition, such oils are preferred which have mixed aniline points below 15 C., and more particularly below 10 C. A mixed aniline point of a given oil is defined as the critical solution temperature of a mixture of 10 cc. of anhydrous aniline, 5 cc. of the oil being tested, and 5 cc. of a naphtha having a straight aniline point of 60 C.

Such oils also are preferred which contain not less than 95%, and more particularly not less than 97%, of aromatic hydrocarbons.

Such oils also are preferred which have densities of not less than 0.95 and, more particularly, not less than 0.98.

These values represent preferred limits for aromatic oils of the type described herein when used for electrical insulating purposes.

As pointed out previously, high-boiling aromatic oils of the type which have been found to be particularly adapted for use as electrical insulating oils may be isolated from the tar or tar emulsion obtained as a result of the pyrolytic decomposition of petroleum, or a fraction thereof, by the flash distillation or more preferably the solvent extraction of the tar or tar emulsion. The extract obtained may be separated into a high boiling and a low boiilng fraction, or other fractions, if desired, after which the high boiling fraction, or the overall extract, may be subjected to polymerization to remove the unsaturated materials present. The oil obtained from such 09- erations then may be refined, such as by sulfuric acid Washing and/or other refining operations, after which the oil may be used as such, or it may be further disitlled and/0r fractionated, or it may be processed otherwise.

The oil obtained from the polymerizing operation also may be treated with clay or other surface active agent, either before or after separation from the polymers, followed by filtration and/or distillation, if desired. Successive clay treatments may be employed.

The preparation of a refined oil of the type more particularly described herein may be illustrated by the following example.

Example 4 A sample of the high-boiling aromatic oils ob tained as in Example 2 and having the following distilling characteristics C. First drop 235 5% 2- .1 10% 243 50% 251 70% 258 73 285 was treated with three successive portitons of 3% by volume of 95.5% sulfuric acid at room temperature. After removing the sludge formed, the oil was diluted by the addition of toluene. The diluted oil then was washed with several successive portions of water, then with a 20% aqueous solution of sodium carbonate, and finally with water until the washings were neutral. The toluene then was removed by distillation at atmospheric pressure, after which the high-boiling aromatic oil was distilled under reduced pressure. A water-white, stable oil possessing excellent dielectric properties thus was obtained.

Aromatic oils of the type described herein, and particularly acid-refined oils of this type, are well adapted for use as electrical insulating oils due to their excellent dielectric properties, due principally to the absence of polar groups, their excellent thermal and electrical stability, their resistance to deterioration under severe service conditions, their low viscosity characteristics, which is of particular importance from the standpoint of their use as transformer or switch oils in which excessive quantities of heat must be dissipated, and to their freedom from free carbon and other extraneous materials.

Hydrocarbon oils used heretofore for electrical insulating purposes have been obtained mainly from two chief sources, namely (1) from coal tar and (2) from petroleum or moderately cracked petroleum products.

Aromatic oils of the type described herein differ fundamentally from such oils in that (1) they are free from the sulfur, oxygen, and/or nitrogen impurities commonly present in oils derived from coal tar and (2) they are derived from petroleum or petroleum fractions by pyroylsis at temperatures greatly in excess of those employed heretofore. This deep cracking, in conjunction with the unique methods developed for the isolation of the said oils, results in the production of aromatic oils remarkably free from impurities. Consequently, such aromatic oils possess unusual dielectric properties.

High-boiling aromatic oils of the type described herein, and particularly refined oils of this type, are well adapted for use as electrical insulating oils for a variety of applications. Thus, such oils may be used as transformer and switch oils, as dielectric oils for oil-filled and/or oil-imprenated high-frequency and/ or high-voltage cables or units, and as impregnating agents for absorbent materials, such as paper and/or cloth, used for electrical insulating purposes, such as for insulating conductors in multiple-wire, or other types, of cables, for the construction of condensers, and the like.

When employing aromatic oils of the type described herein as liquid insulators, such as in switches, transformers, cables, and the like, I generally prefer to have such oils as the sole liquid dielectric present. However, in certain cases it may be found advantageous to have other dielectric oils such as mineral oils, castor oil, hydrogenated castor oil, chlorinated hydrocarbons, for example chlorinated naphthalene, chrinated diphenyl, and ethyl tetrachlorobenzene, present. In all such cases, I prefer to have the high-boiling aromatic oils of the type described herein as the preponderating constituents present.

High-boiling aromatic oils of the type described herein, and particularly refined oils of this type, are unusually well adapted for use as impregnating agents for absorbent materials, such as paper and/or cloth, which are to be used subsequently for electrical insulating purposes. For such impregnating purposes, I prefer to use the said highboiling aromatic oils as the sole liquid dielectric present, although smaller proportions of one or more other liquid dielectrics, particularly those listed previously, may be added to the high-boiling aromatic oil prior to impregnation, if desired.

In certain cases, other liquid dielectric oils may be added to the absorbent material subsequent to impregnation with an aromatic oil of the type described herein.

A preferred embodiment of this invention is the use of a solution of one or more inert resinous and/or plastic material in a high boiling aromatic oil of the type described herein as an electrical insulating composition. Such compositions are particularly desirable for use in impregnating absorbent materials, such as cloth or paper.

Other liquid dielectrics also may be incorpo- 10 rated in such compositions, if desired, particularly when used in minor proportions.

Suitable resinous and/or plastic materials for incorporation in high-boiling aromatic oils of the type described herein, and subsequent use as dielectric compositions, include hydrocarbon resins and/or copolymers, such as those derived by the polymerization of one or more unsaturated hydrocarbons selected from a list comprisin butadiene, isobutylene, butylenes, isoprene, piperylene, cyclopentadiene, amylenes, cyclohexadiene, cyclohexenes, hexadienes, hexenes, styrene, methyl styrene, indene, di-hydronaphthalene, and the like. Polystyrene and polymethylstyrene are preferred resins.

Particularly desirable resins for incorporation in high-boiling aromatic oils of the type described herein are hydrogenated hydrocarbon resins and plastics, such as hydrogenated cyclopentadiene, styrene, methyl styrene, and indene resins. Hexahydro polystyrene and pentahydro polymethylstyrene are preferred resins of this type.

Another suitable resin is that obtained by the polymerization of the high-boiling monomeric material separated from petroleum tar obtained in the pyrolysis of petroleum in the gaseous state in the presence of steam at average set temperatures above 1300 F. The resinous materials obtained in Examples 1, 2, and 3 are of this type. If desired, such resins may be hydrogenated prior to incorporation with the high boiling aromatic oil.

The optimum proportion of resin to aromatic oil of the type described herein will vary somewhat with the nature of the service to which such dielectric blend is to be put. In general, however, I prefer to employ compositions containing at least 50% by weight of an aromatic oil of the type described herein.

Any desired type of absorbent material, such as cloth or paper, may be impregnated with the high-boiling aromatic oil of the type described herein, or with blends of such oils with other liquid and/or solid dielectrics. Kraft paper and linen paper are examples of absorbent materials which are particularly desirable for many electrical uses, such as in the construction of condensers.

The absorbent material may be impregnated in any desired manner. Thus, Kraft or linen paper, or condensers or other insulating units prepared therefrom may be heated under reduced pressure to remove moisture and adsorbed air and other gases, after which the high-boiling aromatic oil of the type described, or a blend of such oil with a liquid and/or solid dielectric, may be introduced into the system, preferably also under reduced pressure, in order to thoroughly impregnate the porous cloth or paper. Paper and/or cloth impregnated in this manner then may be used for any desired insulation purpose, such as in the preparation of condensers.

Paper impregnated with aromatic oils of the type described herein are particularly desirable for use in the fabrication of condensers capable of continuous alternating current operation, due to the excellent thermal stability, and resistance to decomposition, of such oils. Kraft and/or linen paper, impregnated as described, are quite suitable for such use, either alone or in combination with other dielectric materials, such as regenerated cellulose.

Such condensers may be fabricated in any desired manner. Thus, layers of metal foil electrodes, such as aluminum foil may be wound together with a pair of kraft or linen paper spacers impregnated as described previously, after which the finished condenser may be connected with terminals in the usual manner and placed in the usual type of container, such as one of cardboard or metal. An alternative method comprises forming the condenser from paper spacers and metal foil, after which the spacers are impregnated with an aromatic oil of the type described herein, or a dielectric blend containing such oil, the impregnation suitably being carried out under reduced pressure.

The invention may be said to reside more completely in the provision of a high-boiling aromatic oil, the said oil boiling substantially completely above 210 C. and being substantially free from heat-polymerizable and/or reactive materials, possessing unusual stability characteristics when used as an electrical insulating oil. The provision of insulating materials comprising an absorbent material impregnated with an aromatic oil of the type described, and adapted to the fabrication of condensers and other electrical units, also is a feature of this invention.

In the specification and in the claims, the terms aromatic oil boiling above 210 C., aromatic oil boiling above 250 C., and aromatic oil boiling above 275 C. unless otherwise modified, is intended to include the unrefined or refined oil, the preponderating portion of which boils above the indicated temperatures, separated from tar formed during the production of combustible gas by processes involving the pyrolytic decomposition of petroleum oil with or without the aid of catalysts, as well as mixtures of such aromatic oil with the unsaturated aromatic hydrocarbons derived from the same source and/or the resinous polymers derived therefrom.

The term refined aromatic oil refers to an oil of the type described which has been acidwashed, followed by the removal of any acid residues and/or sludge present.

While various procedures and formulas have been particularly described these are of course subject to considerable variation. Therefore, it will be understood that the foregoing specific examples are given by way of illustration, and that changes, omissions, additions, substitutions and/or modifications might be made within the scope of the claims without departing from the spirit of the invention, which is intended to be limited only as required by the prior art.

I claim:

1. As a new composition of matter, an electrical insulating oil comprising castor oil and an aromatic hydrocarbon oil boiling above 210 C., having a mixed aniline point below 15 C., and separated from petroleum oil gas tar.

2. An electrical conductor insulated by material comprising an aromatic hydrocarbon oil boiling above 210 C., containing a mixture of aromatic hydrocarbons constituting at least 95% thereof, having a mixed aniline point below 15 C., and separated from petroleum tar produced in the vapor phase pyrolysis of petroleum oil.

3. A conductor of electricity insulated by material comprising an aromatic hydrocarbon oil boiling above 250 C., containing a mixture of aromatic hydrocarbons constituting at least 95% thereof, having a mixed aniline point below 15 C., having a density of not less than 0.95 and separated from petroleum tar produced in the vapor phase pyrolysis of petroleum oil.

4. An insulated electrical conductor, the insulation of which comprises a hydrocarbon oil fraction of the products of the vapor phase pyrolysis of petroleum oil, said fraction being substantially free from polar groups and heat polymerizable hydrocarbons, and said fraction boiling between 275 C. and 450 C., having a mixed aniline point below 15 C., containing at least of aromatic hydrocarbons, and having a density not less than 0.98.

5. An electrical conductor insulated by material comprising a hydrocarbon resin produced by heat polymerization of a monomeric unsaturated aromatic hydrocarbon material having a preponderant portion boiling between 210 and 350 C. and separated in monomeric form from petroleum oil gas tar and an aromatic hydrocarbon oil boiling above 210 C., and containing a mixture of aromatic hydrocarbons constituting at least 95% thereof, and having a mixed aniline point below 15 C., and obtained from said petroleum oil gas tar.

6. An electrical conductor insulated by material comprising a resinous material and an arcmatic hydrocarbon oil boiling above 210 C., and containing a mixture of aromatic hydrocarbons constituting at least 95% thereof, and having a mixed aniline point below 15 C., and separated from petroleum oil gas tar.

7. Electrical insulation comprising an absorbent material impregnated with an aromatic hydrocarbon oil fraction of the products of the vapor phase pyrolysis of petroleum oil, said fraction containing 95% of a plurality of aromatic hydrocarbons, and boiling above 210 C., having a mixed aniline point below 15 C., and separated from petroleum oil gas tar.

8. As a new composition of matter, an absorbent cellulosic material impregnated with an aromatic hydrocarbon oil fraction of the products of the vapor phase pyrolysis of petroleum oil, said fraction containing 95% of a plurality of aromatic hydrocarbons, and boiling above 210 C., having a mixed aniline point below 15 C. and having a density of at least 0.95.

9. As a new composition of matter, an electrical insulating material comprising paper impregnated with a refined aromatic hydrocarbon oil boiling about 210 C., said oil being a fraction of the products of vapor phase pyrolysis of petroleum oil and containing at least 95% of aromatic hydrocarbons, and having a mixed aniline point below 15 C., and having a density of at least 0.95.

10. As a new composition of matter, an electrical insulating material comprising linen paper impregnated with a refined aromatic hydrocarbon oil boiling above 210 C., said oil being a fraction of the products of vapor phase pyrolysis of petroleum oil and containing at least 95% of aromatic hydrocarbons, and having a mixed aniline point below 15 C., and having a density of at least 0.95.

11. As a new composition of matter, an electrical insulating material comprising kraft paper impregnated with a refined aromatic hydrocarbon oil fraction of petroleum oil gas tar, said fraction boiling above 210 C., having a mixed aniline point below 15 C., and containing at least 95% of a plurality of aromatic hydrocarbons, and having a density of at least 0.95.

12. An electrical conductor insulated by a mineral acid washed aromatic hydrocarbon oil boiling between 210 C. and 450 C., said oil having a mixed aniline point below 15 C., an aromatic hydrocarbon content of at least 95%, a density not less than 0.95, said oil being substantially 13 free from polar groups and heat polymerizable hydrocarbons, and having been separated from petroleum tar produced in the vapor phase pyrolysis of petroleum oil.

FRANK J. SODAY.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 2,266,809 Ruben Dec. 23, 1941 2,150,641 Thomas et a1 Mar. 14, 1939 2,126,937 Weiss Aug. 16, 1938 1,878,509 Michel Sept. 20, 1932 14 Number Name Date 1,856,700 Ford May 3, 1932 2,086,418 Hunt et a1 July 6, 1937 2,073,245 Maibauer Mar. 9, 1937 2,232,761 II. Balthis Feb. 25, 1941 2,220,531 Lazar Nov. 5, 1940 FOREIGN PATENTS Number Country Date 15,309 Great Britain 1899 506,560 Great Britain 1939 15 17, No. 8, Aug. 1928. Translation of an article by Orlov et 81., pages 399 to 405. 

